A Co-locked hairpin probe enabling triple-cascaded signal amplification for the photoelectrochemical detection of dibutyl phthalate.

The sensitive detection of dibutyl phthalate (DBP) is essential for environmental pollution assessment and health risk warning. Although the DNA-based cascade signal amplification strategy can significantly improve the detection sensitivity, non-specific background leakage during amplification remains an unavoidable issue that severely limits the practical performance of sensors. This study developed a co-locked hairpin enabling triple-cascaded signal amplification approach to avoid the non-specific background leakage for ultra-sensitive detection of DBP. Specifically, FeIn2S4/In2O3 heterojunction was constructed to enhance the initial photocurrent signal. Upon activation by the target DBP, the DNAzyme cleaved the co-locked hairpin to release the initiator and fuel strands. These strands further initiated entropy-driven reaction (EDR) to produce the output DNA, which ultimately triggered the hybridization chain reaction (HCR) to generate abundant double-stranded DNA (dsDNA) structures. Subsequently, acridine orange (AO) was intercalated into these HCR-generated dsDNA structures as a photosensitizer to amplify the photocurrent signal. Notably, the co-locked hairpin enabling triple-cascaded signal amplification strategy effectively suppresses non-target signal leakage in the cascade DNA circuit, significantly improving the sensitivity and accuracy of the sensor. The PEC sensor exhibited a linear detection range for DBP from 1 fmol L-1 to 1 nmol L-1, achieving an ultralow detection limit of 0.27 fmol L-1. This study offers a reliable method for precise detection of DBP in the environment and shows promising applications in the field of environmental pollutant monitoring.